The present invention relates to isolated nucleic acid molecules, which encode antigens for Streptococcus agalactiae, which are suitable for use in preparation of pharmaceutical medicaments for the prevention and treatment of bacterial infections caused by Streptococcus agalactiae. 
Streptococcus agalactiae is a gram-positive bacterium, and belongs to the Group B Streptococci (GBS) based on its hemolysis pattern in blood agar. The organism is encapsulated, and capsule is an important element of pathogenicity. Capsules are antigenic and form the basis for classifying GBS by serotypes. Nine distinct GBS serotypes have been identified: Ia, Ib, II, III, IV, V, VI, VII and VIII. Most S. agalactiae serotypes have been shown to cause serious disease, and the two most common serotypes—type III and V—are estimated to account for the majority of invasive disease worldwide. The ranking and serotype prevalence differs by age group and geographic area. In the US, GBS type III causes more than 50% of infant disease, type V about 40% of nonpregnant adult disease, and type Ia about a third of disease in any patient population.
Streptococcus agalactiae is an important agent of human disease at the extremities of age and in those who have underlying disease. Group B Streptococci are the major cause of generalized and focal infections in the newborn infant. GBS is the predominant pathogen in newborns in the US since the 1970's. Bacterial infection can lead to life threatening diseases, such as sepsis, pneumonia and meningitis. Survivors can become permanently handicapped with hearing, learning and visual disabilities. Newborns usually acquire the organism intrapartum or during delivery from their GBS-colonized mothers. In addition, GBS are also a frequent cause of infections in pregnant women and in chronically ill and elderly patients, such as those suffering from diabetes, malignancies, immunodeficiencies, etc., (reviewed by Balter, S. et al. in Gram positive pathogens ed. by Fischetti V. A. et al. ASM Press 2000, pp 154-160).
10-35% of pregnant women are colonized with GBS, but are asymptomatic. However, GBS colonization is important because of the risk of vertical transmission. 50-70% of neonates born to colonized women—that is 5-15% of all newborns—become colonized by GBS during delivery. Colonization is a prerequisite for infection and disease. The most preterm infants are at the highest risk for invasive disease due to low maternal transfer of antibodies and immature immune system. GBS carriage during pregnancy may be chronic, intermittent, or transient. It is difficult to assess the duration of carriage, since women are screened once during a prenatal visit from the late trimester. Several studies suggest that there is a correlation (˜90%) between the colonization status in the third trimester and at the time of delivery. Serotyping of the isolates indicates that persistence of the same type is most common (reviewed by Balter, S. et al. in Gram positive pathogens ed. by Fischetti V. A. et al. ASM Press 2000, pp 154-160).
Without preventive intervention, 1 to 2% of all neonates and 15% of neonates born to heavily colonized women develop invasive disease (sepsis, pneumonia and/or meningitis). In the US, GBS infections affect 1-5 newborns/1000 live birth. About 17.000 cases of invasive GBS disease occurred in the US annually, and 7.500 occurred in newborns before prevention. GBS is the most common cause of bacterial meningitis accounting for ˜40% of all cases reported in this age group. The overall incidence of invasive GBS disease is 0.2-0.7/100.000 in the US. It is somewhat lower in Europe. Mortality without preventive intervention is 6% with invasive disease, every 16. infected newborn dies and 20% of survivors become permanently handicapped.
The rates of serious group B strep infections are much higher among newborns than among any other age group. Nonetheless, serious group B strep infections occur in other age groups in both men and women. Among non-pregnant adults, rates of serious disease range from 4.1 to 7.2 cases per 100,000 populations. The average death rate for invasive infections (infections where the bacteria have entered a part of the body that is normally not exposed to bacteria) is 8-10% for adult's ages 18-64 and 15-25% for adults 65 years of age and over. Mortality rates are lower among younger adults, and adults who do not have other medical conditions. The rate of serious group B strep disease increases with age. The average age of cases in non-pregnant adults is about 60 years old. Most adult group B strep disease occurs in adults who have serious medical conditions. These include: diabetes mellitus; liver disease; history of stroke; history of cancer; or bedsores. Among the elderly, rates of serious group B strep disease are more common among residents of nursing facilities, and among bedridden hospitalized patients. Group B strep disease among non-pregnant adults may often be acquired after recent trauma, or after having certain invasive hospital procedures like surgery ({Farley, M., 2001}; {Jackson, L. et al., 1995}; www.cdc.gov/groupbstrep/).
Direct medical costs of neonatal disease before prevention were $294 million annually and GBS continues to pose a considerable economic burden.
A definitive diagnosis of infection with Streptococcus agalactiae generally relies on isolation of the organism from cervical swabs, blood or other normally sterile body sites. Tests are also available to detect capsular polysaccharide antigen in body fluids.
Penicillin G is the treatment of choice for established cases of GBS. Ten days of treatment is recommended for bacteremia, pneumonia and soft tissue infections, while 2-3 weeks is recommended for meningitis and 3-4 weeks for osteomyelitis.
Prevention has been established since 1994 in North America by screening pregnant women for carriage of GBS, taking vaginal and anorectal swabs at 35-37 weeks' gestation, or by identifying risk factors at admission for delivery without cultures. Women who are candidates for prophylaxis are given intrapartum antibiotic therapy during labor to prevent early-onset neonatal disease. This prevention method has decreased the incidence of GBS disease from 1.7 to 0.4/1000 live births between 1993 and 1999 in the US. Although most neonatal GBS disease can be prevented through intrapartum prophylaxis (Penicillin G or Ampicillin), currently available strategies are not ideal, especially for the prevention of late-onset (>7 days of age) infections and disease in premature babies. There are always individuals who escape of screening for carriage due to several reasons, such as intermittent carriers, who are tested negative at wks 32-35, but become positive during delivery, unattendance, negligence, or delivery before screening date (32-35 wks).
In the long run, widespread use of antibiotics usually induces resistant strains that appear after a period of time. Extensive use of Penicillin (every 3-5th women are treated with high dose), and other antibiotics has already been shown to steadily increase the percentage of antibiotic resistant clinical isolates (ref). Moreover, efficiency of antibiotic based prevention is not that effective for late onset disease, as it is for early onset (within 48 hrs after delivery). An additional concern is that prevention in susceptible adult populations has not been addressed.
Vaccine development is hindered by the lack of sufficient knowledge about the elements of protective immunity against GBS carriage and disease. The relationship of carriage to the development of natural immunity is poorly understood. In addition, the immunologic mechanism that allows disease to occur in a carrier is ill defined. However, it is suggested that the maternal serum levels of pathogen-specific antibodies are correlated with neonatal GBS disease. It has been firmly established that there is an inverse correlation between maternal anti-capsular polysaccharide antibody levels at delivery and the frequency of invasive neonatal diseases {Campbell, J. et al., 2000}.
Although the group B carbohydrate antigen is common to all strains of GBS, unfortunately, it is not strongly immunogenic and antibodies are not protective from lethal challenge in experimental models. The GBS capsule itself that is made of polysaccharides, is immunogenic and is able to induce protective antibodies. However, this protection is type-specific. Although capsular specific antibodies have been shown to be highly protective, it remains unclear what concentration of these serotype-specific antibodies protect against disease and more recently it has become clear that opsonic activity and avidity of these antibodies are more critical determinants of protection than concentration.
The importance of surface proteins in human immunity to S. agalactiae already has been appreciated. It is apparent that all serotypes express surface proteins with activity relevant to host immune defense. The alpha C protein, beta C protein, Rib and Sip proteins are well-characterized biochemically and genetically, and have also been shown to immunogenic and protective in animal models ({Michel, J. et al., 1991}; {Brodeur, B. et al., 2000}; {Larsson, C. et al., 1999}; {Cheng, Q. et al., 2002}). The major problem with these proteins as vaccine candidates seems to be their variability in prevalence among the different clinical isolates of GBS. The Rib protein for example is present in serotype III GBS, but missing from type V, which responsible for significant portion of disease worldwide. Some other surface proteins are characterized as being immunogenic, but there is a limited systematic work done to identify most of the immunogenic proteins of GBS.
Thus, there remains a need for an effective treatment to prevent or ameliorate GBS infections. A vaccine could not only prevent infections by GBS, but more specifically prevent or ameliorate colonization of host tissues (esp. in the birth canal), thereby reducing the incidence of transmission from mother to fetus. Reducing the incidence of acute infection and carriage of the organism would lead to prevention of invasive diseases in newborns—pneumonia, bacteremia, meningitis, and sepsis. Vaccines capable of showing cross-protection against the majority of S. agalactiae strains causing human infections could also be useful to prevent or ameliorate infections caused by all other streptococcal species, namely groups A, C and G.
A vaccine can contain a whole variety of different antigens. Examples of antigens are whole-killed or attenuated organisms, subfractions of these organisms/tissues, proteins, or, in their most simple form, peptides. Antigens can also be recognized by the immune system in form of glycosylated proteins or peptides and may also be or contain polysaccharides or lipids. Short peptides can be used since for example cytotoxic T-cells (CTL) recognize antigens in form of short usually 8-11 amino acids long peptides in conjunction with major histocompatibility complex (MHC). B-cells can recognize linear epitopes as short as 4-5 amino acids, as well as three-dimensional structures (conformational epitopes). In order to obtain sustained, antigen-specific immune responses, adjuvants need to trigger immune cascades that involve all cells of the immune system. Primarily, adjuvants are acting, but are not restricted in their mode of action, on so-called antigen presenting cells (APCs). These cells usually first encounter the antigen(s) followed by presentation of processed or unmodified antigen to immune effector cells. Intermediate cell types may also be involved. Only effector cells with the appropriate specificity are activated in a productive immune response. The adjuvant may also locally retain antigens and co-injected other factors. In addition the adjuvant may act as a chemoattractant for other immune cells or may act locally and/or systemically as a stimulating agent for the immune system.
Vaccine development since the late 1970s has focused on the capsular polysaccharides, but a safe, effective product is still not available. However, vaccine against S. agalactiae is ranked as one of the most important for development and administration to infants and high-risk adults. Currently vaccines against this infection are only in the research stages of development. Efforts are focused on using capsular polysaccharide (CPS) as immunogens, either with or without conjugation to protein {Paoletti, L. et al., 2002}. However, there are several arguments against the use of polysaccharide-based vaccine. Polysaccharides induce IgG2 antibodies, which cross the placenta less efficiently then IgG1 or IgG3 antibodies. It is especially a problem for the most susceptible neonates, the still-borns since placental antibody transfer is low before weeks 32-34. It is estimated that ˜10% of deliveries occur before the 34th pregnancy week.
Protein conjugate vaccines are no doubt a great new addition to the amarmatorium in the battle against GBS disease, but the vaccine can contain only a limited number of GBS serotypes and given adequate ecological pressure, replacement disease by non-vaccine serotypes remains a real threat, particularly in areas with very high disease burden. Moreover, polysaccharide antigens used for active immunization do not provide immunological memory in humans. Conjugation of CPS to non-GBS related immunogenic protein carriers (e.g. tetanus toxoid, cholera toxin B subunit, etc.) has been shown to beneficial in inducing higher concentrations of antibodies in vaccinees, but it does not provide pathogen-specific B cell and T cell epitopes which would recruit memory B and T cells during a real infection to support the most effective host response. To be able to supplement the CPS vaccines with proteins fulfilling these criteria it is necessary to identify conserved immunogenic GBS-specific surface proteins.
All these insufficiencies suggest that there is a need to develop new generation vaccines composed of proteins, or their derivatives, expressed by all strains under in vivo conditions with the ability to induce opsonizing and/or neutralizing antibodies in humans.
There is a great potential for passive antibody-based therapy. There have been already attempts to use human intravenous immunoglobulin (IVIG) preparations for prevention. Recent advances in the technology of monoclonal antibody production provide the means to generate human antibody reagents and reintroduce antibody therapies, while avoiding the toxicities associated with serum therapy. Immunoglobulins are an extremely versatile class of antimicrobial proteins that can be used to prevent and treat emerging infectious diseases. Antibody therapy has been effective against a variety of diverse microorganisms (reviewed in {Burnie, J. et al., 1998}). Anti-GBS mAbs could be given therapeutically to every newborn that develop invasive diseases or preventively to low birth-weight and premature neonates.
During the last decade the immunogenicity and protective capacity of several GBS proteins have been described in animal models and these are now being explored for the development of species-common protein based vaccines. Such proteins are the GBS surface proteins Sip {Brodeur, B. et al., 2000}, rib, □-protein and {Michel, J. et al., 1991}.
Certain proteins or enzymes displayed on the surface of gram-positive organisms significantly contribute to pathogenesis, are involved in the disease process caused by these pathogens. Often, these proteins are involved in direct interactions with host tissues or in concealing the bacterial surface from the host defense mechanisms {Navarre, W. et al., 1999}. S. agalactiae is not an exception in this regard. Several surface proteins are characterized as virulence factors, important for GBS pathogenicity ((reviewed in (Paoletti L. C. et al. in Gram positive pathogens, ed. by Fischetti V. A et al., ASM Press 2000, pp 137-153); {Paoletti, L. et al., 2002}). If antibodies to these proteins could offer better protection to humans then polysaccharides, they could provide the source of a novel, protein-based GBS vaccine to be used in conjunction with or in place of the more traditional capsular polysaccharide vaccine. The use of some of the above-described proteins as antigens for a potential vaccine as well as a number of additional candidates resulted mainly from a selection based on easiness of identification or chance of availability. There is a demand to identify relevant antigens for S. agalactiae in a more comprehensive way.